The present invention relates to document processing along a document transport path, and is particularly directed to a document processing apparatus and method of operating a document processing apparatus.
In some known document feeding mechanisms, there is a need to detect a gap between adjacent documents (i.e., a leading document and a trailing document) which are being fed from an upstream end of a document transport path to a downstream end of the document transport path. In these known document feeding mechanisms, an upstream-located low speed drive transports the leading document along the document transport path until the leading edge of the leading document reaches and engages a downstream-located high speed drive. When the leading edge of the leading document engages the high speed drive, the high speed drive operates to separate the leading document away from the trailing document which is just behind the leading document. As the leading document separates away from the trailing document, a gap is created between the trailing edge of the leading document and the leading edge of the trailing document.
A sensor is positioned along the document transport path to detect presence of the gap formed between the leading and trailing documents. The sensor provides an electrical signal when a gap of sufficient size is detected between the trailing edge of the leading document and the leading edge of the trailing document. Detection of the gap indicates that the leading document has separated away from the low speed drive and that downstream operations (such as aligning the document) can now begin.
A drawback in using gap detection for the purpose of indicating when the leading document is free of the low speed drive is that the size of the gap needs to be large enough so that the sensor can detect presence of the gap. When a relatively large gap is needed, a relatively long document transport path is needed. This is because a document will need to move farther downstream along the document transport path in order to create the relatively large gap. Accordingly, even though a document may be free of the low speed drive, downstream operations cannot begin until a gap of at least a certain size is created between adjacent documents so that the sensor can detect presence of this gap. It would be desirable to provide a way of detecting when a document is free of the low speed drive, without having to wait for a gap of at least a certain size to be created between adjacent documents, so that downstream operations can begin immediately upon detection that the document is free of the low speed drive.